Radar device and method for suppressing interference in a radar device

ABSTRACT

A radar device is described having means ( 10 ) for generating a carrier signal having a carrier frequency f T , means ( 12, 13, 15, 17 ) for generating pulses having a pulse repetition rate f PW , means ( 16 ) for splitting the carrier signal between a transmission branch and a reception branch, means ( 18, 19, 21, 27, 29 ) for delaying the pulses, means ( 24 ) for mixing the carrier signal in the reception branch with a reception signal and means ( 26 ) for integrating the mixed signal, whereby means ( 20, 23 ) for modulating the carrier signal in the transmission branch with the delayed pulses are provided and means for altering the delay in the pulses according to a predetermined code are provided. A method of suppressing interference with the functioning of a radar device is also described.

[0001] The present invention relates to a radar device having means forgenerating a carrier signal having a carrier frequency f_(T), means forgenerating pulses having a pulse repetition rate f_(PW), means forsplitting the carrier signal between a transmission branch and areception branch, means for delaying the pulses, means for mixing thecarrier signal in the reception branch with a reception signal and meansfor integrating the mixed signal. The present invention also relates toa method for suppressing interference with the functioning of a radardevice, including the steps of generating a carrier signal having acarrier frequency f_(T), generating pulses having a pulse repetitionrate f_(PW), splitting the carrier signal between a transmission branchand a reception branch, delaying the pulses, mixing the carrier signalin the reception branch with a reception signal and integrating themixed signal.

BACKGROUND INFORMATION

[0002] Generic radar devices and methods are used for short-rangesensors in motor vehicles, for example. They are used, e.g., to preventaccidents and to detect objects in a dead angle of a motor vehicle.

[0003]FIG. 1 shows schematically the basic design of a radar deviceaccording to the related art. A carrier frequency f_(T) is generated bya local oscillator (LO) 110. This carrier frequency is divided by apower divider 116 between a transmission branch and a reception branch.In addition to carrier frequency f_(T), a pulse repetition rate f_(PW)is supplied by a pulse generator 112 for modulation of the carrierfrequency. In the transmission branch, this modulation is accomplishedwith a switch 120 to which the carrier frequency is applied and which isswitched at the pulse repetition rate. The signal thus generated isemitted by sending aerial 136. Modulation also takes place in thereception branch. However, for the purpose of this modulation, thepulses of the pulse repetition rate are delayed by a delay device 118.Modulation of carrier frequency f_(T) is performed with these delayedpulses by actuation of switch 122 to which the carrier frequency is alsoapplied. In this way, a reference signal S_(R) is made available in thereception branch. This reference signal is mixed in a mixer 124 with areception signal received via receiving aerial 134. The output signal ofmixer 124 is sent to an integration means 126, e.g., a low-pass filterand an amplifier. The signal generated in this way is sent to a signalanalyzer and controller 138, preferably after analog-digital conversion.Signal analyzer and controller 138 then determines the delay of delaydevice 118, this delay being varied between a value Δt_(min) andΔt_(max). For example, the delay may be varied by a microcontroller or adigital signal processor. It is also conceivable to use special hardwarefor this purpose. Then if the transit time of the radar pulses, whichusually corresponds to twice the transit time between the target and theaerial, matches the delay, the amplitude of the output signal of mixer124 is at its maximum. Thus, a correlation receiver is available so thatit is possible that the delay set by controller 138 may be used todeduce the target distance and the radial velocity between the targetand the aerial. FIG. 1 shows as an example only the formation of thein-phase (I) signal. The quadrature (Q) signal is formed in a similarmanner by mixing with the carrier frequency shifted in quadrature.

[0004] It is essentially desirable to suppress interference signals of awide variety of causes. There have already been proposals for utilizingadditional modulation of the microwave signal to separate signalcomponents reflected on targets from interference signals. Inparticular, interference due to other non-coded transmitters, e.g.,radio transmitters, and/or noise is suppressed by such methods.

[0005] However, ambiguities may occur in the determination of targetdistances outside of the unambiguous range of a pulsed radar device. Theambiguity range at target distances r is:

c/(2f _(PW))≦r≦R _(max)

[0006] where

[0007] f_(pw): pulse repetition rate

[0008] c: velocity of light

[0009] R_(max): radar range.

[0010] The following target distances are measured in the ambiguityrange:

{circumflex over (r)}=r−nc/(2f _(PW))

[0011] where n=1, 2, 3, . . . and {circumflex over (r)}≧0.

[0012] In addition, there is interference due to multiple pulse radarsensors operating simultaneously when the sensors are operating withinthe range of another particular sensor. There may be interference, i.e.,for detection of apparent targets. A measured apparent signal delayand/or the corresponding distance from the apparent target will dependon the position between the transmission point in time and the receptionpoint in time of the particular sensors. If one considers sensorsinstalled in different vehicles, for example, it may occur that thesending aerials and receiving aerials of the different sensors areopposite one another. In this case, the interference influence betweenindividual sensors is usually no longer negligible.

ADVANTAGES OF THE INVENTION

[0013] The present invention is based on the generic radar device inthat means for modulating the carrier signal in the transmission branchwith the delayed pulses are provided, and means for altering the delayin the pulses according to a predetermined code are also provided. It ispossible in this way to sample the measurement space, i.e., the periodof time between minimum delay Δt_(min) and maximum delay Δt_(max), notwith a monotonic rise or fall but instead in an order determined by thecode. Such a method of sampling is comparable to random sampling. Aftersampling, the measured values may be ordered according to ascending ordescending values for particular delays Δt so that traditional furtherprocessing of measured values may take place subsequently. This“irregular” sampling is advantageous because mutually interfering radarsensors are usually operated at different points in time so that theyalso detect the measured values for sampling intervals, which areusually different, at a particular point in time. Due to the modulationof the carrier signal in the transmission branch, the time intervalsbetween the radar pulses sent from the various sensors are constantlychanging. Therefore, the measured distances from the apparent targetswhich occur due to the mutual interference of the radar sensors alsochange. Meanwhile, the signal energy of the apparent targets isdistributed over the measurement space, so that the distinction betweenapparent and real targets may be improved. In other words, a separationof signals between different sensors is achieved. If different codes andthus different sequences are used for the sampling intervals formodulation of the transmission point in time with different radarsensors, a further reduction in the influence of interference ispossible. The time intervals between the sampling intervals and theparticular pulses sent previously also change during switching betweenthe particular samplings, so the signal energy of ambiguous targets at adistance r from the transmitter

c/(2f _(PW))≦r≦R _(max)

[0014] is scattered within the measurement space. Since this change inthe time interval takes place only once per switching, it is useful toswitch as frequently as possible. However, the maximum occurrence ofswitching depends on the integration time required for discovery of atarget. Switching for each radar pulse transmitted would be ideal. Thisis possible when the individual pulses have a sufficient signal energyfor single pulse detection, i.e., a sufficient signal-to-noise ratio.

[0015] Means for modulating the carrier signal in the reception branchwith a constant delay are preferably provided. A constant delay may beadequate because the delay in the transmission branch permits avariation and thus a detection of distance. It is thus used only toensure that the reference pulse is always delayed with respect to thepulse transmitted.

[0016] The present invention is particularly advantageous due to thefact that the means for generating a pulse repetition rate f_(PW) have aPN (“pseudo noise”) code generator and the means for delaying the pulseshave means for code shifting. When using such a discrete shift in a PNcode, the delay of the modulation in the reference signal may beomitted. Negative values for the “delay” (advance) in the modulation inthe transmission signal may be calculated in advance and/or adjustedwith the help of the discrete code shift. Through the use of PN codes itis possible to improve the S/N ratio because it is possible to work atan increased pulse repetition rate with PN codes having a suitableautocorrelation function without causing any reduction in the maximumradar range.

[0017] It may be advantageous if means are provided for altering thetransmission points in time and the reception points in time. Inparticular when the delay is accomplished by code shifting, it ispossible to implement different modulation principles in thetransmission branch and in the reception branch, with the modulationoptionally taking place with the differently shifted codes.

[0018] Carrier frequency f_(T) is preferably an integral multiple ofpulse repetition rate f_(PW). Under these conditions, modulation may beimplemented by an integral or half-integral code shift.

[0019] It may be advantageous if means for cyclically altering the codeare provided. This is a suitable option for varying the altered code andthus having an advantageous effect on interference suppression.

[0020] It may be particularly advantageous that means are provided forgenerating ASK (amplitude shift keying)-modulated and/or PSK (phaseshift keying)-modulated signals. Such means result in a furthersuppression of interference effects.

[0021] Furthermore, for the same reason, it may be advantageous if meansfor polarizing the signals are provided.

[0022] The present invention is based on the generic method in that thecarrier signal in the transmission branch is modulated with the delayedpulses, and the delay in the pulses is altered according to apredetermined code. In this way it is possible to sample the measurementspace, i.e., the period of time between minimum delay Δt_(min) andmaximum delay Δt_(max) not rising or falling monotonically but insteadin a sequence determined by the code.

[0023] The carrier signal in the reception branch is preferablymodulated with a constant delay. A constant delay may be sufficientbecause the delay in the transmission branch permits a variation andthus a detection of distance. It is thus used only to ensure that thereference pulse is always delayed with respect to the pulse transmitted.

[0024] It may also be beneficial if a PN (pseudo noise) code isgenerated and if the pulses are delayed by code shifting. In the case ofusing such a discrete shift in a PN code, the delay in modulation may beomitted in the reference signal.

[0025] Negative values for the “delay” (advance) in the modulation inthe transmission signal may be calculated in advance and/or adjustedwith the help of the discrete code shift. Through the use of PN codes itis possible to improve the S/N ratio because in the case of PN codeswith a suitable autocorrelation function it is possible to operate withan increased pulse repetition rate without causing a reduction in themaximum range of the radar.

[0026] It may be beneficial if the transmission points in time and thereception points in time are altered. In particular when the delay isaccomplished by code shifting, it is possible to implement differentmodulation principles in the transmission branch and in the receptionbranch, in which case the modulation may take place with the differentlyshifted codes.

[0027] Carrier frequency f_(T) is preferably an integral multiple ofpulse repetition rate f_(PW). Under these circumstances, modulation maybe implemented by an integral or half-integral code shift.

[0028] It may also be advantageous if the code is cyclically altered.This is a suitable option for varying the altered code and thus havingan advantageous effect on the interference signal suppression.

[0029] It may be beneficial if ASK (amplitude shift keying)-modulatedsignals and/or PSK (phase shift keying)-modulated signals are generated.Such means result in a further suppression of interference effects. Forthe same reason, it may be beneficial if the signals are polarized.

[0030] The present invention is based on the surprising finding thatinterference due to transmission signals from other radar sensors, inparticular similar radar sensors, may be suppressed by coding of thetransmission point in time at the transmitter end. In addition, the riskof overriding of the I channel and/or the Q channel due to mutualinterference of the radar sensors may be reduced. Likewise, signals fromtargets at target distances in the ambiguity range may be suppressed.This method is also advantageously applicable with radar systems whichuse already coded transmission signals and/or reference signalsgenerated, e.g., with the help of PN coding by phase modulation and/oramplitude modulation. Furthermore, it should be emphasized that thelength of the interval required for integration and/or averaging, e.g.,in the case of PN coding, is not influenced. The cutoff frequency of alow-pass filter used for integration may thus remain unchanged and/or beselected with regard to an optimum value for the signal-to-noise ratio.

DRAWINGS

[0031] The present invention will now be explained with reference to theaccompanying drawing on the basis of preferred exemplary embodiments.

[0032]FIG. 1 shows a schematic diagram of a radar device from therelated art;

[0033]FIG. 2 shows a schematic diagram of a radar device according tothe present invention;

[0034]FIG. 3 shows a graphic plot of a signal amplitude to illustrate asampling method;

[0035]FIG. 4 shows a schematic diagram of another radar device accordingto the present invention;

[0036]FIG. 5 shows a schematic diagram of another radar device accordingto the present invention; and

[0037]FIG. 6 shows a schematic diagram of another radar device accordingto the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0038]FIG. 2 shows a schematic diagram of a radar device according tothe present invention. A local oscillator 10 is connected to a powerdivider 16. This power divider 16 is connected to a transmission branch.Part of the power of local oscillator 10 is output by power divider 16into the reception branch. Furthermore, a pulse generator 12 is providedfor generating pulse repetition rate f_(PW). The output of the pulsegenerator is connected to an adjustable delay element 18 and to anadjustable or non-adjustable delay element 19. The output of adjustabledelay element 18 actuates a switch 20 in the transmission branch formodulating the carrier signal. The output signal of the adjustable ornon-adjustable delay element 19 actuates a switch 22 in the receptionbranch for modulating the carrier signal in the reception branch andthus for providing a reference signal S_(R). The signal modulated byswitch 20 in the transmission branch is sent by sending aerial 36 andreflected at a target. This signal is received by a receiving aerial 34and mixed with reference signal S_(R) in a mixer 24. The mixed signal issubsequently sent to a means 26 of integrating, e.g., a low-pass filterand an amplifier. The signal thus generated is sent to a signal analyzerand controller 38 at the input end, adjustable delay element 18 beingcontrolled at the output end.

[0039] Consequently, with the radar device according to FIG. 2, thetransmission points in time may be varied by adjustable delay element18. The delays are in a range of Δt_(S)=0 s . . . Δt_(max)−Δt_(min), andit must be taken into account that non-adjustable delay element 19supplies a delay Δt_(E)=Δt_(max). This fixed delay is useful because thereference pulse must always be delayed with respect to the pulsetransmitted. This yields as total delay Δt=Δt_(E)−Δt_(S)=Δt_(min) . . .Δt_(max). FIG. 2 shows as an example only the formation of the in-phase(I) signal. The quadrature (Q) signal is formed in a similar manner bymixing with the carrier frequency which has been shifted in quadrature.

[0040]FIG. 3 shows how measurement space Δt_(min) . . . Δt_(max) issampled as an example, plotting an amplitude A over signal delay Δt. Inparallel with the delay time axis, a distance axis is also shown,indicating a distance in the range r_(min) . . . r_(max) between thetransmitter and the target. The curve of amplitude A is subdivided intoequidistant intervals, these being parameterized with numbers 1 through16, for example. These numbers indicate the order of sampling. In allintervals, the I and Q output signals of the sensor are detected. Theorder of sampling and thus the value for the delay which is set in eachcase is defined by a suitable code. After sampling, the measured valuesmay be ordered according to ascending or descending values for Δt.Consequently, the measured values may then be processed further in thetraditional way.

[0041] The advantageous effect of sampling, as shown in FIG. 3 forexample, is explained by the fact that the different radar sensors areusually operated at different points in time. Therefore, at a certainpoint in time they detect the measured values for sampling intervalswhich are usually different. Since the time intervals between the radarpulses transmitted by the various sensors change constantly, there isalso a change in the distances from the apparent targets. The signalenergy of the apparent targets is thus distributed over measurementspace Δt_(min) . . . Δt_(max) so that there is a differentiation betweenapparent targets and real targets in an advantageous manner. Likewise,the signal energy of ambiguous targets is scattered within themeasurement space.

[0042]FIG. 4 shows another radar device according to the presentinvention. Elements corresponding to those in FIG. 2 are labeled withidentical reference notation. The particular feature of the embodimentaccording to FIG. 4 is that a PN code generator 13 is provided, thechoice of code being handled by the signal analyzer and controller 38.This code is sent to a code delay 21, where it is delayed in a mannerdetermined by controller 38 in an interval between −Δt_(min) and−Δt_(max). The code is then sent to a modulator 23 in the transmissionbranch. The non-delayed code is transmitted to a modulator 25 in thereception branch, supplying reference signal S_(R) as the output signal.When using a discrete shift in the PN code, the modulation delay in thereference signal may be omitted because negative values for the “delay”(advance) in the modulation in the transmission signal may be calculatedin advance and/or adjusted with the help of the discrete shift. FIG. 4shows only the formation of the in-phase (I) signal. The quadrature (Q)signal is formed in a similar manner by mixing with the carrierfrequency phase shifted in quadrature.

[0043]FIG. 5 shows another embodiment of a radar device according to thepresent invention. Elements corresponding to those from FIGS. 2 and/or 4are labeled with the same reference notation. The special feature of theradar device according to FIG. 5 is that pulse repetition rate f_(PW) isgenerated with the help of a noise generator 15. To suppress frequenciesbelow the maximum Doppler frequency f_(dmax) to be processed, the outputsignal of noise generator 15 may be filtered through a high-pass filter17. As a result, this yields a delay in the transmission points in timeas well as in the reception points in time with a delay time Δt_(mod).In the present case, the radar device is tuned with an adjustable delayelement 27 which controls the carrier signal modulation to generatereference signal S_(R). The radar device according to FIG. 5 permits animproved suppression of ambiguous targets in comparison with the radardevice according to FIG. 2 because the phase angle of pulse repetitionrate f_(PW) is altered from one pulse to the next. Another advantage ofthis radar device is that the remaining signal analysis corresponds tothe related art according to FIG. 1 so that only minor modifications areto be made in the hardware. FIG. 5 also shows as an example only theformation of the in-phase (I) signal. The quadrature (Q) signal isformed in a similar manner by mixing with the carrier frequency shiftedin quadrature.

[0044]FIG. 6 shows another embodiment of a radar device according to thepresent invention where again a PN code generator 13 is provided,supplying the pulse repetition rate to a first means 21 for codeshifting and to a second means 29 for code shifting. Both means 21, 29for code shifting are adjusted by controller 38, which is alsoresponsible for the choice of the PN code. The output signals of means21 for code shifting are sent to a modulator 23 in the transmissionbranch, so that modulation of the carrier signal takes place in thetransmission branch using a code shifted by Δt_(S)=Δt_(mod). In thereception branch, the carrier signal is modulated in a modulator 25using a code which is delayed by Δt_(E)=Δt_(mod)+Δt_(min) . . .Δt_(max), so that a delayed reference signal S_(R) is made available. Ifit is assumed that the carrier frequency is an integral multiple of thepulse repetition rate, then the modulation is implementable, e.g., by anintegral or half-integral code shift. This may be altered, e.g., witheach period of the code used or for each measurement interval. With theradar device according to FIG. 6, for example, only the formation of thein-phase (I) signal has been shown. Again the quadrature (Q) signal isformed in a similar manner by mixing with the carrier frequency shiftedin quadrature.

[0045] The preceding description of the exemplary embodiments accordingto the present invention is given only for the purpose of illustrationand not for the purpose of restricting the present invention. Within thescope of the present invention, various changes and modifications arepossible without going beyond the scope of the present invention or itsequivalents.

What is claimed is:
 1. A radar device comprising means (10) forgenerating a carrier signal having a carrier frequency f_(T), means (12,13, 15, 17) for generating pulses having a pulse repetition rate f_(PW),means (16) for splitting the carrier signal between a transmissionbranch and a reception branch, means (18, 19, 21, 27, 29) for delayingthe pulses, means (24) for mixing the carrier signal in the receptionbranch with a reception signal, and means (26) for integrating the mixedsignal, wherein means (20, 23) for modulating the carrier signal in thetransmission branch with the delayed pulses are provided, and means foraltering the delay in the pulses according to a predetermined code areprovided.
 2. The radar device as recited in claim 1, wherein means (22)are provided for modulating the carrier signal in the reception branchwith a constant delay.
 3. The radar device as recited in claim 1 or 2,wherein the means for generating a pulse repetition rate f_(PW) hd havea PN (pseudo noise) code generator (13) and the means for delaying thepulses have means (21, 29) for code shifting.
 4. The radar device asrecited in one of the preceding claims, wherein means are provided foraltering the transmission points in time and the reception points intime.
 5. The radar device as recited in one of the preceding claims,wherein the carrier frequency f_(T) is an integral multiple of pulserepetition rate f_(PW).
 6. The radar device as recited in one of thepreceding claims, wherein means for cyclically altering the code areprovided.
 7. The radar device as recited in one of the preceding claims,wherein means are provided for generating ASK (amplitude shiftkeying)-modulated signals and/or PSK (phase shift keying)-modulatedsignals.
 8. The radar device as recited in one of the preceding claims,wherein means for polarizing the signals are provided.
 9. A method forsuppressing interference with the functioning of a radar devicecomprising the steps generating a carrier signal having a carrierfrequency f_(T), generating pulses having a pulse repetition ratef_(PW), splitting the carrier signal between a transmission branch and areception branch, delaying the pulses, mixing the carrier signal in thereception branch with a reception signal, and integrating the mixedsignal, wherein the carrier signal in the transmission branch ismodulated with the delayed pulses and the delay in the pulses is alteredaccording to a predetermined code.
 10. The method as recited in claim 9,wherein the carrier signal in the reception branch is modulated with aconstant delay.
 11. The method as recited in claim 9 or 10, wherein a PN(pseudo noise) code is generated, and the pulses are delayed by codeshifting.
 12. The method as recited in one of claims 9 through 11,wherein the transmission points in time and reception points in time arealtered.
 13. The method as recited in one of claims 9 through 12,wherein means (15, 17) are provided for accomplishing a simultaneousmodulation in the transmission and reception branches by phasemodulation or frequency modulation of the pulse repetition rate.
 14. Themethod as recited in one of claims 9 through 13, wherein the carrierfrequency f_(T) is an integral multiple of pulse repetition rate f_(PW).15. The method as recited in one of claims 9 through 14, wherein thecode is cyclically altered.
 16. The method as recited in one of claims 9through 15, wherein ASK (amplitude shift keying)-modulated signalsand/or PSK (phase shift keying)-modulated signals are generated.
 17. Themethod as recited in one of claims 9 through 16, wherein the signals arepolarized.